Hi, software engineer here. The way I see it, opt-out is just a simple check in the system. If somebody introduces a bug in the code and that opt-out doesn't work for even a few minutes... all your data can potentially be scraped. And then it's probably too late to fetch your data out of the ai... Also people are talking about only public information will be scraped, but they keep forgetting that most have their faces in their publicly available profile picture... Private messages I think are different, because they are not posts they are messages in the messenger.
I personally deleted all of my pictures and posts and will only be using the messenger going forward, since my family doesn't want to move to another chat service...
Luckily the one you wrote on https://www.reddit.com/r/BoycottUnitedStates/comments/1jrcrh6/lemmy_as_an_nonus_alternative_to_red_dit_using/ is still there :)